Spontaneous potential measurement apparatus connected between me

Electricity: measuring and testing – Of geophysical surface or subsurface in situ – Using electrode arrays – circuits – structure – or supports

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324366, G01V 318, G01V 320

Patent

active

054020697

ABSTRACT:
A spontaneous potential (SP) sub is interconnected between two metallic housings of a wellbore apparatus and is lowered into a wellbore. A spontaneous potential (SP) of an earth formation trasversed by the wellbore is measured by the SP sub, and a log is generated from the sub which is representative of the spontaneous potential of the formation, the log being substantially free of a special type of distortion which typified the prior art SP measurements taken by prior art SP measurement apparatus. The SP sub includes a measurement electrode, monitoring electrodes placed on both sides of the measurement electrode, a bucking electrode placed on both sides of the monitoring electrodes, current driving circuitry connected to the bucking electrodes, and receiving circuitry connected to the monitoring electrodes. The current driving circuitry delivers a current of sufficient magnitude to each bucking electrode such that the voltage potential between the monitoring electrodes is approximately equal to zero. The current from each bucking electrode is grounded via its own respective metallic housing and not via a surface oriented electrode. The receiving circuitry monitors the voltage between each of the monitoring electrodes and looks for a zero potential difference between the monitoring electrodes. When the receiving circuitry locates the zero potential difference at a moment in time between its monitoring electrodes, the measurement of the spontaneous potential taken by the measurement electrode at that same precise moment in time is received and recorded. A plurality of such measurements made by the measurement electrode represents a log of spontaneous potential of the earth formation traversed by the wellbore which is substantially free of the distortion which typified the prior art SP log measurements.

REFERENCES:
patent: 2592125 (1952-04-01), Doll
patent: 3638105 (1972-01-01), Schuster
patent: 3638106 (1972-01-01), Cram
patent: 3798533 (1974-03-01), Schuster
patent: 3798534 (1974-03-01), Schuster
patent: 3882376 (1975-05-01), Schuster
Technical Publication No. 2463 "The S.P. Log: Theoretical Analysis & Principles of Interpretation" by H. G. Doll, New York Meeting, Feb. 1948, AIME.
"Selective SP Logging" by H. G. Doll, Member AIME, Schlumberger Well Surveying Corp., Ridgefield, Conn., vol. 189, 1950, pp. 129-142, Petroleum Transactions, AIME.
"SP Deconvolution and Quantitative Interpretation in Shaly Sands". buy J. R. Tabanou, SWS; R. Glowinski, UH; G. F. Rouault, SWS; The Log Analyst Sep.-Oct. 1988, pp. 332-344.

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